The most critical of the environmental threats for your piano
is the humidity. Which is measured in degrees of Relative
Himidity (RH), most pianos are ment to be kept at 42
degrees RH but, since every instrument is unique, is always a
good idea to ask your tuner-technichan.

As
described by the Piano
Technicians Guild website: “Relative humidity (RH) is
the amount of moisture contained in the air, compared to the maximum
amount of moisture that the air is capable of holding”.

As
for sound and action, excessive dryness causes the piano's pitch
to go flat, while high moisture levels make the pitch go sharp.
Also, changes in humidity will make the wooden parts to swell
and shrink, affecting tuning stability and touch.

Furthermore,
not only the sound is altered, but also the piano itself
is harmed: Excessive moisture will swell the wood and
rust the strings and all metal parts, while excessive dryness
will distort your piano’s soundboard and weaken its glue
joints. Repeated changes in the humidity levels will eventually
render your piano useless. That is why a precise climate control
is so important.

Depending
on your needs and possibilities, there are several ways to keep
RH under control:

The
most effective is the “Climate Control System”
which, installed inside the piano, will keep it within the factory
suggested limits. This is the most recommended solution because
it’s specifically designed for pianos.

The
system consists of a series of dehumidifier rods (depending on
your instrument and levels of humidity, could be one or more),
a humidifier (if needed), and a humidistat (a control unit, which
depending on the environment turns on and off the dehumidifier
and/or the humidifier).